Evaporation and Salinity swing

Been reading how much water evaporate on people's sump. A lot of them are around 1 gallon/day. That's about 7 gallon/week. Will this actually swing the salinity? Unless you do water change weekly, then I thought it would change the salinity.

 

Most of us have auto top offs that top off freshwater (ro/di) as the evaporation happens so there is no swing

 

I know that salt will stay as the water evaporates. However, if there are a lot of RO replacing it, I thought eventually it will change the salinity. Specially for those small tanks.

 

Depending on the tank it can be a severe or small swing. I have a ATO as said above.

 

I can't speak for a small tank. I went 4 weeks without a water chamge only topping of my ato res and didn't have any change in salinity, with 85 gallons total volume. Maybe someone with a small tank can chime in

 

if you have an ATO, you wouldn't have an issue with swings. This is what the top off is for. One a larger system though, 1 gallon per day or even 7 gallons isn't going to make that much of a difference. I evaporate about 2 - 3 gallons per day or even more, btw.

 

As water evaporates, salinity rises. When you top off, you bring it back to normal. My 29g loses 2 - 3 cups per day. I top off manually each evening, and the salinity "swing" isn't noticeable with a floating glass hydrometer. The only way your salinity would change over time is if you are losing saltwater through spray (like using an airstone with an open top) or excessive wet skimming along with not doing water changes.

 

I don't have ATO so I keep mine at 1.024 so when it evaporates then it won't go to high. Mines a 56g so I don't lose much water either.